Bailey was listed by the Observer as one of the 50 funniest acts in British comedy in 2003. In 2007 and again in 2010, he was voted the 7th greatest stand-up comic on Channel 4's 100 Greatest Stand-Ups.[4]

Bailey was born in Bath, Somerset, and spent most of his childhood in Keynsham, a town situated between Bath and Bristol in the West of England. His father was a medical practitioner and his mother was a hospital ward sister. His maternal grandparents lived in an annexe, built on the side of the house by his maternal grandfather who was a stonemason and builder. Two rooms at the front of the family house were for his father's surgery.[5]

Bailey was educated at King Edward's School, an independent school in Bath[6] where he was initially a highly academic pupil winning most of the prizes. At about the age of 15, he started to become distracted from school work when he realised the thrill of performance as a member of a school band called Behind Closed Doors, which played mostly original work. He was the only pupil at his school to study A-level music and he passed with an A grade. He also claims to have been good at sport (captain of KES 2nd XI cricket team 1982), which often surprised his teachers. He would often combine music and sport by leading the singing on the long coach trip back from away rugby fixtures. It was here that he was given his nickname Bill by his music teacher, Ian Phipps, for being able to play the song "Won't You Come Home Bill Bailey" so well on the guitar.[5]

He started studies for an English degree at Westfield College of the University of London but left after a year.[7] He is a classically trained musician and received an Associateship Diploma from the London College of Music as well as being made an honorary member of the Society of Crematorium Organists. He performed with a boy band "The Famous Five".[8]

Bailey often mythologises his early years in his stand-up. In his show Bewilderness, he claims to have attended Bovington Gurney School of Performing Arts and Owl Sanctuary. He talks about a succession of jobs he had before becoming a comedian, including lounge pianist, crematorium organist, door-to-door door-salesman and accompanist for a mind-reading dog. A clip of Bailey's appearance in the dog's routine was shown during his Room 101 appearance.

Bailey began touring the country with comedians such as Mark Lamarr. In 1984 he formed a double act, the Rubber Bishops, with Toby Longworth (a former fellow pupil at King Edward's, Bath). It was there that Bailey began developing his own unique style, mixing in musical parodies with deconstructions of or variations on traditional jokes ("How many amoebas does it take to change a lightbulb? One, no two! No four! No eight..."). According to comedy folklore, after a reviewer once criticised his act for its lack of jokes, Bailey returned the following night, at Queen Margaret College, Edinburgh, to perform a set composed entirely of punchlines. Longworth left to join the RSC in 1989 and was replaced by Martin Stubbs.

Stubbs later quit to pursue a more serious career, and in 1994 Bailey performed Rock at the Edinburgh Festival Fringe with Sean Lock, a show about an ageing rockstar and his roadie, script-edited by comedy writer Jim Miller. It was later serialised for the Mark Radcliffe show on BBC Radio 1. The show's attendances were not impressive and on one occasion the only person in the audience was comedian Dominic Holland. Bailey almost gave up comedy to take up a telesales job.[21]

He went solo the next year with the one man show Bill Bailey's Cosmic Jam. The show led to a recording at the Bloomsbury Theatre in London which was broadcast in 1997 on Channel 4 as a one-hour special called Bill Bailey Live. It was not until 2005 that this was released on DVD uncut and under its original title. It marked the first time that Bailey had been able to tie together his music and post-moderngags with the whimsical rambling style he is now known for.

Though he did not win the Perrier in 1996, the nomination was enough to get him noticed, and in 1998 the BBC gave him his own television show, Is It Bill Bailey?.

This was not Bailey's first foray into television. His debut was on the children's TV show Motormouth in the late 1980s – playing piano for a mind-reading dog. Bailey reminisced about the experience on the BBC show Room 101 with Paul Merton in 2000. In 1991, he was appearing in stand-up shows such as The Happening, Packing Them In, The Stand Up Show and The Comedy Store. He also appeared as captain on two panel games, an ITV music quiz pilot called Pop Dogs, and the Channel 4 science fiction quiz show Space Cadets. Is it Bill Bailey? was the first time he had written and presented his own show.

Over the next few years, Bailey made guest appearances on shows such as Have I Got News for You, World Cup Comedy, Room 101, Des O'Connor Tonight, Coast to Coast and three episodes of off-beat Channel 4 sitcom Spaced, in which he played comic-shop manager Bilbo Bagshot.

In 1998, Dylan Moran approached him with the pilot script for Black Books, a Channel 4 sitcom about a cold-hearted bookshop owner, his nice-guy assistant, and their socially awkward female friend. It was commissioned in 2000, and Bailey took the part of the assistant Manny Bianco, with Moran playing the owner Bernard and Tamsin Greig the friend, Fran. Three series of six episodes each were made.

When Sean Hughes left his long-term role as a team captain on Never Mind the Buzzcocks in 2002, Bailey became his successor. His style quickly blended into the show, possibly helped by his background in music. He soon developed a rapport with host Mark Lamarr, who continually teased him about his looks and his pre-occupation with woodland animals. It was announced on 18 September 2008 that Bailey would be leaving the series and be replaced by a series of guest captains including Jack Dee and Dermot O'Leary.[22] Whilst touring in 2009, Bailey joked that his main reason for leaving the show was a lack of desire to continue humming Britney Spears' Toxic to little known figures in the indie music scene. During this time he also left his position as "curator" of the Museum of Curiosity, and declared his intention to "retire" from panel games, although he has since appeared on QI many more times and hosted Have I Got News For You.

Bailey also presented Wild Thing I Love You which began on Channel 4 on 15 October 2006. The series focuses on the protection of Britain's wild animals, and has included rehoming badgers, owls and water voles.

Bailey appeared in the second series of the E4 teenage "dramedy" Skins playing Maxxie's dad, Walter Oliver. In episode 1, Walter struggles with his son's desire to be a dancer, instead wishing him to become a builder, which is what he himself does for a living. Walter is married to Jackie, played by Fiona Allen.

As a continuation of Bailey's recent foray into natural history, he presented ITV1's half-hour wildlife mini-series Baboons With Bill Bailey.[24] The series was filmed in Cape Town and spanned 8 episodes, with exclusive content available on itvWILD.[25]

In 2009, Bailey presented a project about the explorer and naturalist Alfred Russel Wallace, in the form of an Indonesian travelogue.[26] Bailey said in an interview that Wallace had been "airbrushed out of history", and that he feels a "real affinity" with him. In 2013, to coincide with the centenary of Wallace's death, Bailey presented a two-part documentary, Bill Bailey's Jungle Hero, first broadcast on BBC Two on 21 and 28 April 2013.[27] He travelled around producing and filming the series in Indonesia and Borneo.[28]

In 2001, Bailey began touring the globe with Bewilderness. A recording of a performance in Swansea was released on DVD the same year, and the show was broadcast on Channel 4 that Christmas. A modified version of it also proved successful in America, and in 2002 Bailey released a CD of a recording at the WestBeth Theatre in New York City. The show contained his popular music parodies (such as Unisex Chip Shop, a Billy Bragg tribute, which he also performed with Bragg himself at the 2005 Glastonbury Festival), "three men in a pub" jokes (including one in the style of Geoffrey Chaucer) and deconstructions of television themes such as Countdown and The Magic Roundabout. A Bewilderness CD was sold outside gigs, a mixture of studio recordings of songs and monologues Bailey had performed in the past – it was later released in shops as Bill Bailey: The Ultimate Collection... Ever!. That same year he also presented a Channel 4 countdown, Top Ten Prog Rock.

Bailey premiered his show Part Troll at the 2003 Edinburgh Festival Fringe. A critical and commercial success, he then transferred it to the West End, where tickets sold out in under 24 hours, and new dates had to be added. Since then he has toured it all over the UK as well as in the US, Australia and New Zealand. Bailey expanded on subjects such as the war on Iraq. He also talks extensively about drugs, at one point asking the audience to name different ways of baking cannabis. A DVD was released in 2004.

Bailey appeared at the Beautiful Days festival in August 2007. The UK leg of the Tinselworm tour enjoyed 3 sell-out nights at the MEN Arena in Manchester, Europe's largest indoor arena, and culminated with a sell-out performance at Wembley Arena.

Early in 2007, a petition was started to express fans' wishes to see him cast as a dwarf in the The Hobbit films, after his stand-up routine mentioned auditioning for Gimli in The Lord of the Rings. The petition reached its goal in the early days of January, and was sent to the producers. It was hoped that as the Tinselworm tour took him to Wellington in New Zealand where the film was in pre-production, that he would be able to audition.[29]

A minor part in Simon Pegg's and Edgar Wright's film Hot Fuzz, as a pair of desk sergeant twins (Bailey had originally meant to also appear in Pegg and Wright's earlier film, Shaun of the Dead, but the commentary included with the DVD of that movie explains that he was busy with other commitments at the time)

March: Appeared at the International Human Beatbox Convention at the Southbank Centre in London, introducing Shlomo to the stage for the climax of the concert, as well as showing off his own beatboxing

7 September: Guest on live Australian TV show Rove.[30] In a questionnaire to win 20 dollars in 20 seconds, host Rove McManus asked his usual question, "Who would you turn gay for?" Bailey replied, "The pope"

Bailey is a talented pianist and guitarist and has perfect pitch; of this he has said

"Perfect pitch ... occurs entirely at random in about one in every 10,000 of us, and I'm one of them. From as early as I can remember, I was able to pick out the pitch of things, not just instruments but washing machines, vacuum cleaners, dentists' drills."[33]

His stand-up routines often feature music from genres such as jazz, rock (most notably prog rock from the early seventies), drum'n'bass, rave, classical, and even theme songs, usually for comic value. Favourite instruments include the keyboard, guitar, theremin, kazoo and bongos. He also mentioned in an interview that he has achieved Grade 6 Clarinet. He was part of punk band Beergut 100,[34] which he founded in 1995 with comedy writer Jim Miller and also featured Martin Trenaman and Phil Whelans, with Kevin Eldon as lead singer.[35] The band performed at the 2006 Edinburgh Festival Fringe.[36] Trenaman and Welans had previously appeared in Cosmic Jam under the name "The Stan Ellis Experiment", and Trenaman and Eldon later featured with John Moloney in the Kraftwerk homage "Das Hokey Kokey" on the Part Troll tour. Bailey claims that he and the three other performers are a Kraftwerk tribute band called Augenblick. To mark the final gig of the Part Troll tour on 1 January 2005, the band reappeared on stage after the "Das Hokey Kokey" joke to play an hour-long encore of music.